1. Field of the Invention
The present invention relates to a fluid valve control system, which is adapted to freely set and control the control characteristics of the fluid valve by the generation of pulses based on stored table data.
2. Description of the Prior Art
Heretofore, a fluid-controlled valve has been controlled by a feedback control method utilizing an analog system. According to the feedback control method utilizing an analog system, however, control patterns for actuating a fluid-controlled valve so as to have a prescribed opening, i.e. the kinds of opening variations relative to the time base for switching a valve so as to have a prescribed opening, are limited to a linear pattern and an exponential function pattern which makes use of the charging and discharging of a capacitor. For this reason, it has been impossible to freely set a control pattern to meet the characteristics to be controlled.
In recent years, a valve whose opening can be adjusted by digital control, a so-called digital valve, has been made fit for practical use. Therefore, it has been made possible to optionally set a control pattern by the step control of a pulse motor.
However, since the conventional control systems for a digital valve are limited to either a constant speed control system using drive pulses of a constant frequency or a constant acceleration control system making the pulse interval of drive pulses variable, a control pattern has to be set by inputting via a keyboard, for example, the number of steps per unit time until the opening of the valve reaches the prescribed opening in order to freely set a control pattern, thereby making the setting of a pattern very complicated.
When the set opening is to be varied without changing the shape of a control pattern, it is necessary to redo a control pattern every time that a set opening is varied, thereby making it difficult to easily vary the set opening.
These problems are also applicable to a digital valve for use in pressure control, which utilizes a pulse motor for varying the set spring load of a relief valve.
On the other hand, fluid-controlled valves adopting the conventional analog system, such as servo valves, proportional control valves, for example, require a control accuracy which is as high as the aforementioned digital valves and must cause the control characteristics to be freely set in a manner similar to that of the digital valves.
In a hydraulic system using this kind of fluid-controlled valve, the control of a fluid is generally carried out automatically in accordance with the procedures for operating a programmable sequencer. However, a programmable sequencer is classified into two types, one type functioning so as to read a numerical value set by a switch of an operation panel, and then convert a decimal code into a binary code, and then issue an output, and the other type having no such function. In order to effect a digital control, a conversion into a binary code is required. A programmable sequencer of a simple type having no function for converting a decimal code into a binary code cannot be used in digital control without requiring modification thereto. Thus, digital control can be effected only with a programmable sequencer having the conversion function and raises a problem in that such sequences are not in wide use.